1. Field of the Invention
The present invention relates to an engine control system and, more particularly, to improvements of an engine control system for suppressing a slip by reducing torque of the engine when the vehicle body causes a slip.
2. Description of the Related Art
Heretofore, for example, Japanese Patent Unexamined Publication No. (Kokai) 63-5,116 discloses the technology of suppressing a slip of the vehicle body by reducing torque of the engine by restricting the super-charging action, i.e. when the action of increasing the power of the engine by supplying fuel or air above the normal pressure, when a slip of the vehicle body is detected on the basis of a difference between driven and undriven (following) wheels of the vehicle. Further, it is known that the slip can be suppressed by reducing torque of the engine by ceasing the supply of fuel to a portion of cylinders or by retarding the timing of ignition, when the vehicle body causes a slip.
The slip of the vehicle body can be suppressed with high responsiveness when the supply of fuel to the cylinders of the engine is ceased or when the timing of ignition is retarded. On the other hand, responsiveness cannot be said sufficient when the slip of the vehicle body is suppressed by restricting the supercharging action, for example, by reducing the supercharging pressure, i.e. the pressure to be supercharged or to be increased above the normal pressure, by opening a bypath control valve disposed for bypassing a mechanical supercharger, because an operation of the bypath control valve is delayed to some extent. For this reason, generally, higher demands are made to suppress the slip of the vehicle body by ceasing the supply of fuel or by retarding the timing of ignition or by combining them than by restricting the supercharging action.
For an internal combustion engine with a supercharger, however, an after-burning phenomenon is caused to occur if the supply of fuel to a portion of the cylinders is ceased in a supercharging region in which the rate of intake air is high, thereby elevating the temperature of the exhaust gases and adversely affecting thermal durability of an exhaust system, an after-burning phenomenon being the event that unburned ingredients of exhaust gases withdrawn from the cylinders of the engine, where combustion is being carried out in normal conditions, are caused to be burned in an exhaust passage as a result of reaction with oxygen present therein in a high concentration. Even when the timing of ignition is retarded in a supercharging region where the power of the engine is increased above the normal pressure, with the attempt to suppress the slip of the vehicle body, such an after-burning phenomenon may likewise be caused to occur resulting in exerting an adverse influence upon thermal durability. Accordingly, the idea may arise that, for an internal combustion engine with a supercharger, the slip of the vehicle body is to be suppressed by restricting the supercharging operation in such a supercharging region and by ceasing the supply of fuel or retarding the timing of ignition in a non-supercharging region where no pressure is to be supercharged or the power of the engine should not be increased above the normal pressure.
With the arrangement of a slip control system for an internal combustion engine with a mechanical supercharger such that the slip can be reduced in the supercharging region by restricting the supercharging operation and in the non-supercharging region by ceasing the supply of fuel or retarding the timing of ignition, however, problems may occur that the extent to which the slip of the vehicle body is caused to be reduced may be worsened if the vehicle would be accelerated during a period of time when the slip is still being controlled in the non-supercharging region by ceasing the supply of fuel to the cylinders of the engine and/or by retarding the timing of ignition and, consequently, if the non-supercharging region would be shifted to the supercharging region. Upon the shift into the supercharging region, the control of the slip is also required in usual cases to be shifted to a fashion in which the slip is to be reduced by restricting the supercharging operation; however, as described hereinabove, the mechanical supercharger may cause a delay in starting the operation for restricting the supercharging operation of the engine. As a result, no slip can be controlled until the supercharging operation is begun and, on the contrary, the slip may be caused to be increased again even once the slip is going to be reduced by ceasing the supply of fuel or by retarding the timing of ignition, thereby impairing the extent of convergence of the slip.